Miata Technical
Service Bulletin

Category

Applicable Model(s)

Subject

Bulletin No.

001/90

Issued

6/8/90

Revised

G

1986 -'90 RX-7 & MX-5 Miata

Timing Light Malfunction

Description

A Distributor-Less Ignition system (DLI) has been adopted in
the RX-7 and MX-5 Miata since 1986 production. On a DLI system,
discharge from the ignition coil is bipolar - one side is
negative, the other positive. Therefore, if a timing light is
designed to meet discharge from the negative terminal only, it
will not light or will light intermittently at the positive
terminal.

This condition is not a result of a vehicle
malfunction, it is a problem with the design of the timing light.
Please pay close attention to this situation to avoid
misdiagnosis.

Check your timing light on an RX-7 or MX-5 Miata to see
if it lights correctly on each cylinder. The light should
work from either the positive or negative side. If it
does light correctly, it can be used on a DLI system. If
it does not light correctly, do not use it on a DLI
system.

When purchasing a new timing light, perform the test
mentioned above to determine whether or not the timing
light can be used on a DLI system.